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| Titel |
Vibrational properties of silica species in MgO-SiO2 glasses from ab initio molecular dynamics |
| VerfasserIn |
G. Spiekermann, M. Steele-MacInnis, P. M. Kowalski, C Schmidt, S. Jahn |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068293
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| Zusammenfassung |
| Glasses and melts in the system MgO-SiO2 are analogs for magmas of the Earth’s mantle.
Therefore knowledge of the structure of these glasses and melts is important for
understanding numerous geological processes. Raman spectroscopy is useful for probing the
atomic-scale structure of glasses and melts. However, correct assignment of observed
vibrational bands to specific structural and modal origins is challenging. We present the
mode-projection technique to calculate vibrational subspectra for specific modal vibrations of
several fundamental silica structures in silicate glasses. Structural subunits that
we have studied include Q0 to Q4 tetrahedra, Si-O-Si bridging oxygen atoms for
any degree of polymerization of the adjacent tetrahedra, the ethane-like symmetry
of the dimer, and three- and four-fold rings. We apply this technique to ab initio
molecular dynamics (MD) trajectories of MgO-SiO2 glasses at 1000 K. We found the
tetrahedral symmetric stretch at 863 cm-1 for Q0, 885 cm-1 for Q1, a double peak of
960 cm-1 and 1037 cm-1 for Q2, 1032 cm-1 for Q3 and 1080 cm-1 for Q4. The
bridging oxygen asymmetric stretch is at about 980 cm-1 for Q1-Q1, and it shifts to
about 1100 cm-1 with increasing polymerization. This analysis has applications
especially for understanding the structure of silica-poor glasses. For instance, two
contradicting Raman spectroscopy studies of Mg2SiO4 glasses reported the most
polymerized SiO4 tetrahedra in the glass structure to be either Q0 [1] or Q3 [2]. Our
results indicate that the degree of polymerization is overestimated, if the Si-O-Si
stretching modes are not considered in the interpretation of the measured Raman
spectra.
[1] Nasikas, N. K. and Chrissanthopoulos, A. and Bouropoulos, N. and Sen, S. and
Papatheodorou, G. N., 2011, Chemistry of Materials 23, 3692-3697.
[2] Kalampounias, A. G. and Nasikas, N. K. and Papatheodorou, G. N., 2009, Journal of
Chemical Physics 131, 114513. |
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